In general, the present invention relates to aluminum sheet metal materials for metallic containers and components thereof, compositions thereof, and methods and processes of manufacture thereof enabling and facilitating the manufacture of containers and the like by use of materials of used empty containers and scrap materials as part of a recycling system.
At the present time, substantial efforts are being made to conserve energy and material resources as well as to eliminate waste and litter problems which have long plagued the beverage industry in particular. The present invention is part of an attempt to develop a total recycle program in the aluminum can industry including: (1) the collection and return of aluminum beverage cans after use by the consumer; and (2) the re-use of the aluminum material of used cans to manufacture new cans. Thus, the primary purpose of the present invention is to provide an economically feasible recycle program for aluminum beverage cans. The primary purpose has been fulfilled by development of a new aluminum alloy composition enabling the manufacture of all components of aluminum cans from a single alloy composition by new methods and processes which provide single alloy composition sheet stock suitable for use with conventional aluminum can making equipment, methods and processes. As a result of the use of the new composition and the new methods and processes, an aluminum can having all components made from sheet stock of the same alloy composition may be produced by high speed mass production techniques whereas, in the past, different components of commercially acceptable aluminum cans have been made from different alloy compositions such as shown in the following Table I:
TABLE I __________________________________________________________________________ Others Alloy Silicon Iron Copper Manganese Magnesium Chromium Zinc Titanium Each Total __________________________________________________________________________ AA 3003 0.6 0.7 0.05- 0.2 1.0-1.5 -- -- 0.10 -- 0.05 0.15 AA 3004 0.30 0.70 0.25 1.0-1.5 0.8-1.3 -- 0.25 -- 0.05 0.15 AA 5182 0.20 0.35 0.15 0.20-0.50 4.0-5.0 0.10 0.25 0.10 0.05 0.15 AA 5082 0.20 0.35 0.15 0.15 4.0-5.0 0.15 0.25 0.10 0.05 0.15 AA 5052 0.45 Si + Fe 0.10 0.10 2.2-2.8 0.15-0.35 0.10 -- 0.05 0.15 CS42 0.20 0.35 0.15 0.20-0.50 3.0-4.0 0.10 0.25 0.10 0.05 0.15 __________________________________________________________________________
The numerical amounts shown represent weight percentages. The ranges shown are inclusive. These conventions are carried throughout the present specification. All percentages shown above are maximums unless a range is shown. The AA designation and number refer to the registration of the alloy with the Aluminum Association. CS42 refers to an Alcoa alloy developed for use in can ends and tabs and further described below.
Aluminum food and beverage containers have been successfully manufactured since the early 1960s. As used herein, the term "container" refers to any aluminum sheet product formed to contain a product, including carbonated beverage cans, vacuum cans, trays, dishes, and container components such as fully removable ends and ring tab ends. The term "can" refers to a fully enclosed container designed to withstand internal and external pressure, such as vacuum and beverage cans. Initially only can ends were formed of aluminum and were termed "soft tops". These tops had no easy opening features and were manufactured from Aluminum Association (AA alloy) 5086. The introduction of easy opening ends such as the "ring pull" end required the use of more formable alloys such as AA 5182, 5082 and 5052. The commonly used 5082 and 5182 are high in magnesium content (4.0-5.0%) and are designed to be relatively strong as compared to those alloys used in can bodies. 5052 is primarily used in shallow drawn and drawn and redrawn non-pressurized containers, as it lacks sufficient strength for most can applications.
Shortly after the introduction of aluminum can ends, aluminum can bodies were introduced. Aluminum can bodies were initially made as parts of three piece cans, as "tin" cans had traditionally been made. Three piece cans consist of two ends and a body which is formed into a cylindrical shape and seamed. Two piece cans have since been developed and are gradually replacing three piece cans in beverage applications. Two piece cans consists of a top end and a seamless body with an integral bottom end. Two piece can bodies are formed by a number of processes, including shallow drawing, drawing and redrawing, and drawing-and-ironing.
An apparatus for making drawn-and-ironed cans is described in U.S. Pat. No. 3,402,591, to which attention is directed for a further understanding of the can body manufacturing aspect of the present invention. In drawing and ironing, the body is made from a circular sheet, or blank, which is first drawn into a cup. The side walls are then extended and thinned by passing the cup through a series of dies with diminishing bores. The dies produce an ironing effect which lengthens the side walls and permits the manufacture of can bodies having sidewalls thinner than their bottoms. AA 3004 is typically used in the formation of two piece can bodies, as it provides adequate formability, strength, and tool wear characteristics for the draw-and-iron process. These properties are a function of the low Mg (0.8-1.3%) and Mn (1.0-1.5%) content of the alloy.
The presently used 3004 is disadvantageous in that it requires a high ingot preheat or homogenization temperature for a long time in order to achieve the desired final properties. Conventional ingot preheating is one of the most costly factors in producing finished sheet. In addition, 3004 has a relatively slow casting rate and a tendency to form large primary segregation when improperly cast.
Other alloys have been previously considered for use in can bodies, such as AA 3003. This alloy meets all forming requirements for the draw-and-iron process, but was abandoned because of low strength at economical gauges.
The conventional alloys described above for can ends and can bodies differ significantly in composition. In the manufactured can, the end and the body are essentially inseparable so that an economical recycle system requires use of the entire can. Therefore, in recycling cans, the melt composition differs significantly from the compositions of both conventional can end alloys and conventional can body alloys. If it is desired to obtain the original compositions, significant amounts of primary, or pure, aluminium must be added to obtain a conventional can body alloy composition, and even greater amounts of primary aluminum must be added to obtain a conventional can end alloy composition.
Accordingly, it would be advantageous to employ an aluminum alloy of the same composition in both can ends and can bodies so that the remelt from those cans would not have to be adjusted. This advantage was recognized and described by Setzer et al. in U.S. Pat. No. 3,787,248, which proposes a can end and body which are both made from a 3004 type alloy which has been heat treated to provide the formability necessary for its use in can ends. The fabrication process proposed by Setzer et al., however, includes a high temperature holding step after cold rolling. Furthermore, the compositions proposed by Setzer et al. would produce a melt composition significantly different from a melt of conventional two alloy cans.